A variety of different sizes and shapes of aluminum framing components are commonly used in the construction of pool, patio and glass enclosures. Historically 2.times.2 hollow aluminum extrusions (which typically have outside dimensions of 1.98 inches.times.1.98 inches) have had the widest applications in these installations, being used in screen enclosures for pools as purlins, chair rails and top rails, and as uprights at corners and around doorways, and being used in screen and glass rooms or patio enclosures as top rails, beams, chair rails and uprights and the like. Of course, standard industry tolerances apply to all extrusion dimensions set forth in this application.
The standard 2.times.2 hollow aluminum extrusions currently in use have four internal screw bosses, two on each side wall, intended to receive fasteners for anchoring the extrusions to other framing components. A drawback to this design is that sometimes the contractor installs less than four fasteners, which can have an adverse effect on the structural load capacity and thus the span capability of the extrusion. A minimum of three tightly secured fasteners is required to prevent the extrusions from rocking under load.
Another drawback to the standard 2.times.2 hollow aluminum extrusions is that the fasteners either have a tendency to strip out of the screw bosses, or a twist condition occurs when the fasteners are run into the screw bosses, resulting in noticeable lines in the side walls of the extrusions behind the screw bosses which are unacceptable from an aesthetics standpoint in that the lines make it appear as if the fasteners are breaking out of the extrusion walls.
Another aluminum framing component that is widely used in screened patio and pool enclosures to hold the screens in at the top and bottom edges and at the corners of the enclosure is a 1.times.2 open back aluminum extrusion, which typically has outside dimensions of 0.990 inch.times.1.98 inches. The standard 1.times.2 open back aluminum extrusions include two internal screw bosses that are sometimes used to anchor the extrusions to other framing components. However, the screw bosses in the open back extrusions can be a hindrance especially when attaching the ends of hollow aluminum extrusions to the face of the open back extrusions by running fasteners through the face into the screw bosses in the hollow aluminum extrusions in that the screw bosses in the open back extrusions prevent the fasteners from being flush mounted up against the inside surface of the face of the hollow aluminum extrusions, thus necessitating the use of longer fasteners.